We continued our studies on the physiological role and mode of replication of the choline-containing pneumococcal teichoic acids. The specific achievements of last years' work were as follows: 1) identification of a minor portion of cellular choline (5-15% of total) as a component of the heterophyle (Forssman) antigen. (The major portion of cellular choline is component of the cellular C-antigen.) This substance seems to be a lipoteichoic acid. 2) By using specific enzymatic degradation methods we started a detailed comparison of the primary structures of cell walls from choline containing versus ethanolamine containing cells. The aim of these studies is to elucidate the mechanism of lysis resistance that cells with ethanolamine containing cell walls exhibit when treated with antibiotics or detergents. 3) We isolated pneumococcal bacteriophages and we are using these for the functional characterization of cell surface components.